Low cost actuator with 2 dimensional motion

ABSTRACT

A two dimensional actuator from a substrate and arranged to bend orthogonal portions of said substrate so as to cause a combined two-dimensional motion of the substrate that is defined by the relative excitation of orthogonal portion actuators.

The use of piezo actuators as motion systems is known, as is theirincorporation into frames for the provision of multiple axis actuation.This approach is adequate for the location of high cost actuators inapplications such as laser positioners, where cost is secondary toaccuracy and force.

Simple bender constructions can be assembled to provide multiple axismotion but the labour content of such assemblies rapidly outpaces thecosts of the actuators themselves. The use of pivots is extremelyundesirable in these circumstances, due to the small motion available tothe actuators. To provide a low friction pivot of say 3 mm diameter, itis necessary to have at least 50 microns of freeplay between the movingparts, and this represents a significant percentage of the availablemotion. To provide 2 dimensions of motion in this way the linkage willhave a minimum of 100 microns of float. Float can be reduced through theuse needle pivots and flexing hinges but these have high cost andstiffness respectively.

Thus, the object of the present invention is to provide a low costactuator with reduced pivot losses.

According to the present invention there is provided an actuator formedfrom a substrate and arranged to bend orthogonal portion of saidsubstrate so as to cause a combined two-dimensional motion of thesubstrate that is defined by the relative excitation of orthogonalportion actuators.

In order that the present invention be more readily understood,embodiments thereof will now be described with reference to theaccompanying drawings, in which:—

FIG. 1 is a perspective view of a U-shaped substrate for use in thepresent invention;

FIG. 2 is a perspective view of the substrate shown in FIG. 1 in anintermediate condition;

FIG. 3 is a perspective view of the substrate shown in FIG. 2 withpiezo-ceramic material attached;

FIG. 4 is a diagram for explaining the motion of the end of thesubstrate shown in FIG. 3;

FIG. 5 is a diagram for explaining further motion of the end of thesubstrate shown in FIG. 3;

FIG. 6 is a perspective view of a modification to the substrate shown inFIG. 2;

FIG. 7 is a perspective view of an etched plate which may be utilised bythe present invention; and

FIG. 8 is a side view of the etched plate in FIG. 7.

FIG. 9 is a side view of a hairpin arrangement using the etched plateshown in FIG. 7.

The present invention provides an active material actuator that utilisesthe d31 mode of operation to bend multiple and orthogonal portions of alaminar substrate to provide a combined XY motion that is defined by therelative excitation of the orthogonal portion actuators.

A suitable substrate such as kovar metal is formed as shown in FIG. 1.The shape comprises four planar surfaces (10 a-10 d) where two surfaces(10 a,10 b) are colinear and these two sets of colinear surfaces areseparated by a bridging portion (30) to form a flat U-shape. To aid theformation of the final shape the area (20 a) between the two colinearsurfaces (10 a,10 b) and the area (20 b) between the two colinearsurfaces (10 c,10 d) can helpfully be thinned by either acid etching orreduction by a necking punch, but this is not essential to the operationof the final device save in that it will affect the stiffness andappropriate measures must be taken to maintain the stiffness.

A series of folding operations are now performed upon the flat shape.Each leg is folded at the centre of the area (20 a,20 b) between thecolinear portions, but one part is folded upwards and the other isfolded downwards. A further orthogonal bend is made in the centre of thebridging portion (30) to create the form shown in FIG. 2.

In FIG. 3 each of the planar surfaces (10) now has adhered to it a poledpiezo ceramic plate (40). The technology of both adhesion and themanufacture of the piezo ceramic plates is known and does not requirespecific discussion here. The plates are fixed to the outer surfaces ofthe folded portions to form two hairpin shapes that open outwards whenthe piezo ceramic plates are excited by the application of a suitablevoltage. The plates 40 can be adhered prior to folding if desired.

FIG. 4 shows the motion of the individual hairpins as they are excited.This motion is commonly termed d₃₁ actuation because it is thecontraction of the second and third dimensions in response to theincrease of the third plane that is used. The third plane is the planeof the field, hence the terms 31, 32 and 33, where the first digitsignifies the applied field direction and the second digit describes themotion plane.

Consider now the behaviour of a point on the free end (50) of the secondactuator (50) when the system is fixed at the other free end (60).Excitation of the first hairpin (70) will cause the point (50) to risein the Y plane. The elevation will be directly proportional to theapplied charge, within the limits of material hysteresis and otherlimitations, up to the maximum strain achievable with the specificmaterial. Consider now the application of a second charge to the plateson the second hairpin (80) which is perpendicular to the first. Thenotional spot (50) will now move in the X plane.

It is a useful feature of piezo and other electro ceramic actuators thattheir shape change is proportional to the applied field.Electro-strictive and piezo electric materials respond to electricfield, whilst magneto-strictive materials respond to magnetic fields.Any such materials can be usefully substituted for the describedmaterials to respond to one or more stimuli. For example, the positionof the point (50) can be determined by one magnetic and one electrostrictive actuator to measure two phenomena.

The proportional or near proportional nature of the described materialsmakes it possible to apply known levels of stimulus to the two actuatorsand to position the notional spot (50) anywhere in a box the size of thestroke limit of each actuator. This makes the actuator suitable for thepositioning of fibreoptics, for example, moving a signal fibre between anumber of receivers.

Consider further the coordinated stimulation of the two actuators by asimple sinusoidal signal. If the input to one actuator is sinusoidal andthe input to the second is synchronous but inverted the net position ofthe notional point will describe a circle proportional to the signalamplitude. This motion is shown in FIG. 5. In order to maintain acircular action the start point for the circle requires an initialexcitation of the vertical actuator (70) to the target radius.

To make a simple motor the combined output can be attached to a crankhaving a radius equivalent to one half of the total available stroke.The output from the crank is simply converted to a motor output by theaffixation of a flywheel or gear. To make a vibration motor the outputshaft can simply be fitted to a rotating eccentric.

The available force from each actuator will not be equal because thevertical actuator has to lift the lateral one, assuming that gravity isworking in the normal direction. Even if the parts are oriented tocompensate for the gravitational effects the stiffness of the firstactuator must be higher to drive the increased mass of the secondactuator.

FIG. 6 shows an improved construction wherein the lifter actuatorcomprises two hairpins 70 a, 70 b separated by a slot 90. The slot maybe inserted in the upper surface 71 or lower surface 72 of the lifteractuator. Additionally, the surfaces 71,72 of each hairpin 70 a,70 b mayhave adhered to them a poled piezo ceramic plate.

It is beneficial and superior for the lower actuator to comprisemultiple hairpins rather than simply using wider plates because themultiple plates have the same anisotropy as the single plates and so thestroke is maintained whilst increasing the force output.

Alternatively, the multiple plate arrangement of FIG. 6 may be formedfrom two slotted substrates being placed one over the other with theirslots in register and whose end portions are connected together at oneend to form a hairpin.

It will be appreciated that the multiple plate arrangement may have anunlimited number of hairpins being formed as the lifter actuator, eachhairpin being separated by a slot 90. The slot extends along the uppersurface 71 and has a corresponding slot on the lower surface 72 but isof a length such that there is a rigid connection between each hairpinat each end of the slot. Furthermore, the multiple hairpin arrangementdescribed above may be utilised in the other orthogonal actuator 80.

In addition, it is advantageous but not essential for each hairpin tohave adhered to it an electro ceramic plate which is preferably a piezoceramic plate FIG. 7 shows a plate 75 which may be used in the presentinvention. The plate 75 has an etched portion 76 and a plurality ofslots 90, in this case two slots separating three surfaces 75 a,75 b,75c of the plate 75. The underside of each surface 75 a,75 b,75 c may haveadhered to it a piezo-ceramic plate 45 to provide movement of the plate75 when the piezo ceramic plate 45 is excited. The piezo plate ispreferably of a size such that it extends beyond the width x of theetched portion 76 as shown in FIG. 8.

The etched portion 76 of the plate 75 may have a layer of metal such ascopper within the etched portion to compensate for the thermal effectscaused by differences between the coefficient of thermal expansion ofthe plate 75 in that of the piezo plate. Additionally, the plate 75 istypically formed from a substrate such as kovar. The etching process isknown in the art so will not be discussed in detail herein, howeveretching is typically achieved using chemical etching or electrochemicalmachining.

The plate 75 may be utilised in the present invention by acting as thelifter actuator 70 but may also provide a replacement for the otherorthogonal actuator 80. The construction of this type of etched plate 75with slots 90 allows for multiple plates to be formed from one metalsubstrate thus providing less resistance to deflection from stiffness aswould be the case with a single plate.

FIG. 9 shows an embodiment of the hairpin arrangement which is formedwhen the etched plate is utilised as an orthogonal actuator in thepresent invention.

The hairpin arranged is formed using two etched plates 75 in aconfiguration so that the etched portion 76 of each plate 75 faces oneanother. Furthermore, the slots of one plate are positioned so as todirectly correspond to the slots of the other plate. The length of eachslot is to the extent that it does not reach the peripheral areas 77which are the unetched respective ends of the plate 75. Thus, the slotsextend only within the width of the etched portion of the plate.Additionally, the end of the slots will be shaped but preferablyrounded.

Both the etched plates are bounded together to form the hairpin at oneof the facing peripheral ends 77 of each etched plate. Accordingly therewill exist a gap 43 between the plates at the opposite peripheral end.

The outer surfaces 74 of each etched plate 75 may have adhered to it anelectro ceramic plate 45 such as a piezo ceramic plate with the lengthof the piezo plate extending beyond of the length of each slot and on tothe peripheral areas 77.

A useful feature of the plate 75 is that it may be of any length andslots can be inserted into the plate depending on the force which isrequired when the piezo ceramic plates attached to the plate 75 areexcited. Furthermore, the slots 90 provide uniform behaviour along thelength of the plate 75 and length is proportional to strength.

Although the hairpin arrangement in FIG. 9 shows the use of two etchedplates being connected together at one end to form a hairpin, thehairpin may be formed from one plate with separate etched portions. Theplate may be folded about an area separating the etched portions so asto form a hairpin arrangement from a single plate hence removing theneed to band more than one plate together.

It will be appreciated that the construction described in FIGS. 7 and 8may be used independently from the folded construction described aboveto provide an actuator with increased force output due to the use of aplate with multiple slots.

1. An actuator arrangement formed from a substrate folded to form orthogonal portions; and each provided with a controllable actuation layer to form an actuator; whereby a combined two-dimensional motion of a part of the substrate by relative excitation of the orthogonal portion actuators.
 2. An actuator arrangement according to claim 1 wherein the two dimensional motion is an XY motion such that one end of the substrate moves in the Y plane when a first orthogonal portion actuator is excited and said end of the substrate moves in the X plane when a second orthogonal portion actuator is excited.
 3. An actuator arrangement according to claim 1, wherein the actuation layer of at least one of said orthogonal portion actuators is a piezo-electric layer.
 4. An actuator arrangement according to claim 1, wherein the actuation layer of at least one of said orthogonal portion actuators is a magneto-strictive layer.
 5. An actuator arrangement according to claim 1 which utilizes the d31 mode of operation.
 6. An actuator arrangement according to claim 1 wherein each of the orthogonal portions are in the shape of a hairpin.
 7. An actuator arrangement according to claim 6 wherein at least one of the orthogonal portions comprises multiple hairpins separated by slots.
 8. A piezo ceramic actuator comprising a planar metal member provided with an elongate slot which is parallel to one edge of the member and is located wholly within the periphery of the member whereby to create end portions at each end of the slot and form a plurality of actuator sections.
 9. An actuator according to claim 8 wherein two planar metal members are placed one over the other with their slots in register and whose end portions are connected together at one end to form a hairpin.
 10. An actuator according to claim 8 wherein actuator layers are formed on the planar metal member on either side of the slot or each slot.
 11. An actuator according to claim 8, wherein the actuation layer is a piezo-electric layer.
 12. An actuator according to claim 8, wherein the actuation layer is a magnetostrictive layer.
 13. A actuator according to claim 10 wherein one major surface of the planar metal plate is reduced in thickness between the end portions.
 14. An actuator according to claim 13 wherein the reduced thickness portion is provided with a layer of metal in order to alter the thermal characteristics of the metal member.
 15. An actuator according to claim 14 wherein the metal is copper.
 16. An actuator according to claim 13 wherein the actuator layers extend beyond the length of the slot or each slot and on to the end portions. 